Clamping tube for thread millers and the like



P. w. MARHN.

CLAMPI NG TUBE FOR THREAD MILLERS AND THE LIKE.

Patented Apr. 11, 1922.

2 SHtETS-SHEET 1.

APPLlCATION HLED JUNE 22, 1920.

P. w. MARTIN. CLAMPING TUBE FOR THREAD MILLERS AND THE LIKE. APPLICATION FILED JUNE 22,1920- 1A=12,809 Patented Apr. 11, 1922.

2 $HEETS$HEET Z- 10 13 Fig. 3

r STATES earnnr caries.

PERCY W. MARTIN, OE BAY CITY, MICHIGAN, ASSIGNOR TO SMALLEY GENERAL COMPANY, OF BAY CITY, MICHIGAN, A CORPORATION OF MICHIGAN.

CLAMI ING- TUBE FOR THREAD MILLERS AND THE LIKE.

Lari Bees.

Specification of Letters Patent.

Patented Apr. it, 1%;22.

Original application filed May 24, 1918, Serial No. 236,334. Divided and this application filed June 22,

" 1920. Serial No. 390,845.

To all to 710m it may concern Be it known that I, Pnnor TV. MARTIN,

citizen of the United States, residing at Bay City, in the county of Bay and State of Michigan, have invented certain new and useful Improvements in Clamping Tubes for Thread Millers and the like; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

7 This invention. relates to improvements in thread milling machines, lathes and the like and pertains more particularly to improved means whereby the cutting hob may be quickly and accurately located in operative invention is applicable is of the utmost importance in practice, because there are many classes of work in which it is imperative that the commencement of the thread in the finished work shall be exactly in the same position on successive pieces of work. For example, in the cutting of threads on the jaws 0r chasers commonly used in dies for cutting pipe threads and the like, it is essential not only that the threadsbe cut accurately on the successive chasers comprising a set, but, in order that corresponding chasers taken from different sets of chasers may be interchangeable, it is also absolutely necessary that the threads on the corresponding chasers commence at exactly the same point. 7

Otherwise, if, say, the number 2- chaser of one set were taken out and the number 2 chaser of another set were substituted for it, and if the threads on the two number 2 chasers did not commence at exactly the same point on both, the completed set of chasers when assembled in a die stock would .not cut a proper thread, the reason being that the number 2 chaser of the second set would not track with number 1 and number 3 chasers of the first set, and the number 2 chaser of the second set would, therefore, pare the thread in the finished work. In other words, the corresponding chasers of successively manufactured sets are ordinarily not interchangeable and consequently it has heretofore been necessary when one chaser of a set became damaged to discard the entire set, the cause of such imperfection" being that the successively manufactured chasers did not have their threads commence at exactly the same point, and this variation was generally caused by the presence of backlash in the cutting mechanism of the milling machine or lathe in which the chasers were threaded.

There are many other examples of classes of work in which it is essential that the threads be accurately started and that threads in successive pieces of work be com menced at exactly the same location on the successive pieces/ It is also necessary to avoid back-lash in the rapid production of' perfect threads in other classes of commercial work, such as pipe threads, bolts, etc, aside from the manufacture of chasers.

It is not possible in a thread-miller which has back-lash in its feed mechanism to rapidly produce duplicate work that meets the above rigid requirements, because the lead is usually thrown into action in such machines by clamping the'lead-screw by means of a threaded s lit nut or its equivalent. "When such a split nut is thrown into engagement with the lead-screw it frequently happens that the threads of the nut do not come fair with the threads on the lead-screw and consequently gripping action between the nut and lead-screw is not instantaneously accomplished and the clamping action is accompanied by a slight relative movement of the lead screw and nut when the two threads come together.

With myimproved device I am enabled to instantly grip the stationary and moving members, so that feed starts instantly. The gripping action can take place at any point whatsoever in relation to the lead screw, without having to wait until after the abovementioned relative longitudinal movement of the lead screw and nut has taken place. Even though the back-lash may be only of the same.

The claims ofthis case are directed to specific embodiments of my device and the equivalents thereof.

Broader aspects of the invention are presented in my copending application, Serial l'lo; 236,83t, filed May 241-, 1918, to which reference may be had, this being a continuation of said application.

In that application, one form of connection between the lead-screw and the hobcarriage is shown.

In the present application 1 am presenting a modified form embodying certain im provements in construction while providing for the effective elimination of back-lash.

Nith the foregoing and certain other objects in view, which will appear later in the specification, my invention comprises the devices described and claimed and the equivalents thereof.

In the drawings, Fig. 1 is a top plan view of a thread-miller embodying my improvement.

Fig. 2 is a longitudinal sectional elevation Fig. 3 is a detached view partly in section, showing the lead-screw'with its ing nut and clamp.

Fig. 1 is an end view of the clamp.

Fig. 5' is a perspective detail of the cage forming a part of a preferred form of frictional bearing for the traveling tube.

Fig. 6 is a diagrammatic view of a thread miller chuck with chaser blanks in position to be cut, and showing the starting position of the hob circumferentially with respect to ,which is actuated by the main driving gear 3, the spindle being revolvably mounted in suitable bearings 4L and 5.

A cutting-hob 6 carried by a hub spindle 7 and actuated by a drive pulley 8 is mounted in the usual transverse carriage 9, this carriage being in turn mounted upon a longitudinally movable carriage 10 adapted to be moved backand-forth by the usual traversingwheel 11, which is adapted to actuate the carriage along its guides 12, 12 and 13, 13 by means of a suitably connected rack and pinion, not shown.

Rotatably mounted in bearings 14 carried travelby the base 1 is the lead screw 15, adapted to be rotated by a train of drive gears16, actuated from the main spindle 2.

A nut 17 is threaded on the lead screw 15 and is secured to a traveling tube 18,

which encloses the lead screw. The outer surface of the traveling tube is adapted to be releasably gripped by a clamp 19 carried by the longitudinally movable carriage .10.

This clamp is preferably in the form of a slotted band, one of the ends of the band being threaded as at 20, Fig. 4E, and adapt ed to be clamped by means of'a threaded screw 21, one end of which is swiveled, as at 22. in the clamp 19.

Referring now to Figs. 3 and 1, it is seen that when the clamp 19 is tightened-so as to grip the traveling tube 18 and hold it against turning, the continued rotation of lead-screw 15 will impart lead to the longitudinally movable carriage 10 and'to the tween the working surfaces, or through jar, 1

accident or otherwise. I

When clamp 19 is again engaged to startthe movement of lead a small amount, sometimes as much as threeor four-thousandths of an inch, of back-lash or lost motion is apt to be found between the lead screw thread and the nut 17 if means isjnot provided to prevent this. 7

My present invention provides means for automatically preventing the occurrence-of back-lash, that is to say, for automatically preventing any relative movement taking place between the lead screw 15 and the nut 17 when the clamp 19 is released from and subsequently'gripped to the tube 18.

It is apparent that if the contact between the screw 15 and nut 17 were capable of being maintained so that just the proper amount of frictional contact would always occur between them, no further means would need to be provided to prevent their relative movement when clamp 19 is released or tightened; but since it is not possible in practice to maintain such thread-contact permanently I provide means for effecting by being inserted in longitudinal slots 25 hob cn'cuini'erentially, as at A, a mark or of a sleeve or bushing 26, Fig.6, which is received in the bore ot tube The end of the tube is preferably closed. by a bushing 27.

The blocks 23, being yieldingly pressed against the surface oi": the spindle of lead screw 15 exert suflicient friction to insure that tube 18 will revolve with screw 15 as soon as clamp 19 is released, without altering in the slightest the relative positionsof the screw 15 and its nut 17. Thus, when clamp 19 is again tightened, no relative motion or backlash can occur between screw 15 and nut 17 and carriage 10 and its hob 6 will commence to move immediately the clamp 19 is tightened.

The absence of back-lash is due to the fact that the frictional engagement between the blocks 28 and the spindle of the screw keeps the two working surfaces of the threads or" the screw 15 and nut 17 always in working contact.

In the production by the thread-milling process, oi successive sets of chasers which shall be so accurately produced that any chaser of one set can be used interchangeably with the corresponding chaser of any other set, it is of course necessary that the cutting hob shall not only have the proper axial or lengthwise motion of lead with respect to the rotation of the work, but also that in the cutting of each successive set of chasers the hob will always commence its out at exactly the same point on each chaser.

This condition is illustrated diagrammatically in Figs. 6 and 7.

Referring to Fig. 6, a, b, c, and (Z represent four chasers of a set to be cut by means of the multiple tooth revolving hob 6. The hob is first run radially to its cutting position by proper adjustment of the carriage 9see Fig. 2, the clamp 19 is gripped to the traveling tube 18, and the main spindle 2 is started. This simultaneously starts the lead screw 15 and imparts to the hob 6 its longitudinal or lead movement in the direction of the arrow in Fig. 7.

It is obvious that one set of chasers a, Z), 0, (Z, can be properly cut with one or more revolutions of the work, but after this set is finished and a new set of blank chasers is inserted in the chuck, it will not be possible to thread the individual chasers or the second set so that they will operate interchangeably with the corresponding individual chasers of the first set, unless prior to the commencement of cutting the second set, the hob 6 is initially located in exactly the same position radially with respect to the work, as indicated a A in Fig. 6, and unless the hob is also located in exactly the same position longitudinally with respect to the work, as in Fig. 7 on both the first and second settings of the machine.

To ei'l'ect the proper initial placing of the index is preferably placed upon the chuck. and after the work is clamped in the chuck, the chuck is turned until the position of the mark A coincides radially with the po sition of the hob 6, as shown in Fig. 6. Then, before the machine is started, the hob (5 is properly located longitudinally with respect to the work. The clamp 19 is then tightened to grip the tube 18.

Any desired means of locating the longitudinal starting position of hob 6 may be employed, but I prefer to use the means shown in Fig 7, where 28 is the chuck in which the chasers a, b, 0, (Z, are mounted,

and 29 is a hardened steel stop-pin fixed to the chuck 28.

By placing a suitable piece of metal called a teeler between the face of pin 29 and the end oi hob 6, a fixed distance 30 is established. Distance 30 being established, and radial position of the hob and work as indicated at A in Fig. 6, being also established, as by the means hereinbefore described, and back-lash or play between the threads of lead screw 15 and nut 17 having been eliminated, is then perfectly certain that each chaser of the set a, b, c, at, will be a duplicate of and interchangeable with the corresponding chaser of any other subsequently formed set of chasers.

It will be noted that whenever the tube 18 is rotated with the lead screw there is no relative longitudinal movement between the tube and the lead screw, but whenever the tube is clamped and the lead screw is revolved, then there is a longitudinal movement between the tube and the screw and when the tube has reached the end of the screw it is necessary to return it to its original position by rotating the screw by hand, while preventing the tube from rotating.

in practical use of this class of machines it is sometimes desirable to rotate the main spindle 2 without using the lead screw, and in that case it is advantageous to not run the tube along the lead screw thread, which would make it necessary to oftener return the tube by hand as above noted. Consequently my improved construction provides that when the tube is not clamped it will revolve with the lead screw, and since under these circumstances there is no relative motion between the lead screw and the tube, the tube will maintain its longitudinal position on the screw until it is again caused to operate in conjunction with the lead screw by tightening clamp 19.

While I have chosen the cutting of a chaser as an illustration of the necessity of avoiding back-lash and of the necessity in certain classes of duplicating work of always starting the cut by first establishing the same circumferential and longitudinal positions of the hob and the work, yet it will be readily understood, as above noted, that the same requirements prevail in duplicating many other classes of thread-milling work, to all of which my present invention is well adapted. 7

Having thus described myinvention, what I claim and desire to secure by Letters Patent is; v

1. In a thread-milling machine the combination of a lead screw, a nut threaded to said lead screw, a traveling tube enclosing the lead screw and fixed to said nut, a clamp fixed to the tool carriage of the machine and adapted to releasably grip said tube, and means adapted to frictionally engage said tube and lead screw, to prevent relative movement therebetween when said clamp is disengaged.

2. In athread-milling machine the combination of a lead screw, a nut threaded to said lead screw, a traveling tube enclosing the led screw and fixed, at one end, to

said nut, a clamp fixed to the tool carriage of said machine and adapted to releasably grip said tube, and friction members yieldrevolvable work-holding chuck and'a cutting hob, the combination of a lead screw, a nut threaded to said lead screw, a traveling tube enclosing the lead screw and fixed to the nut, a clamp fixed to the tool carriage of the machine and adapted to releas'ably grip said tube, means adapted to frictionally engage said tube and lead screw, together with a stop carried by said work-holding chuck and adapted to engage the end of said hob, whereby to gauge the commencement of the cut when said clamp is caused togrip said tube, for the purposes set forth.

In testimony whereof I aflix my signature.

PERCY w. MARTIN. 

